Artificial resistance.



No. 792,638. PATENTED JUNE 20, 1905. W R WHITNEY ARTIFICIAL RESISTANCE.

APPLICATION FILED NOV.16, 1901. RENEWED KOV.3.1904.

Figl.

NO. 792,638. Patented June 20, 1905.

UNITED STATES PATENT OFFICE.

WVILLIS R. WVHITNEY, OF BOSTON, MASSACHUSETTS, ASSIGNOR TO GEN- ERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ARTIFICIAL RESISTANCE.

SPECIFICATION forming part of Letters Patent No. 792,638, dated June 20, 1905.

Application filed November 16,1901. Renewed November 3,1904. Serial No. 231,205.

T (I'll whom it y 007103771" sistance-body is exposed to an intense heat in Be it known that I, WILLIS R. WHITNEY, a the presence of air. The conducting material citizen of the United States, residing at Boson the surface of the body is thereby burned ton, in the county of Suffolk, State of Massaaway, leaving the binding substance in the 5 chusetts, have invented certain new and useform of baked clay or porcelain. The depth ful Improvements in Artificial Resistances, of to which the conducting substance is burned which the following is a specification. away may be varied by varying the length of Electrical resistances are frequentlyformed heating of the resistance-body, as will be eviof mixtures of graphite, carbon-dust, or other dent.

I conducting material with some binding sub- By the application of this method resistancestance, such as ordinary clay or the constitubodies, such as pencils, may be made in large ents of which porcelain is made. The subquantities and all of substantiallyuniform restances chosen are formed while in a plastic sistance. If desired, the exposed layer of state into the desired shapes and are then dried baked clay or porcelain forming the outside I 5 and baked. Such artificial resistances, usually of the resistance-pencils may be covered with in the form'of rods, are largely used in the a glaze. IVhether or not a glaze is used, the construction of lightning-arresters, as resistouter surface of the resistance device, being ances for electrical measuring instruments, more or less vitrified, furnishes a good pro- &c. In many cases it is desirable to produce tection against dampness, and so tends to pre- 20 large numbers of these resistance devices each serve a uniform resistance of the device.

of the same size and shape, composition, and The novel features which characterize my resistance. It has been found in practice, invention I have set forth with particularity however, that even though the composition of in the appended claims. the resistance devices, such as rods, be as For a detailed description of my invention 2 5 nearly as possible the same in all the rods the reference is to be had to the following speciresistances of the rods will vary very greatly. fication, taken in connection with the accom- 7 5 Thus, for example, some of the rods, which panying drawings, in whichare to all appearances identical with others, Figure 1 represents one of the many utilimay diifer in resistance by fifty or seventyties of which my invention is capable, and

30 five per cent, or even much more. Ihave dis- Fig. 2 is a perspective view of a resistancecovered that in resistance-bodies of the charpencil made in accordance with my invention.

acter mentioned the conductivity, such as it Fig. 1 represents a lightning-arrester of is, often resides very largely in the surface well-known type in which the current-limitcoating or skin of the body and that if this ing resistance 1 is constructed in accordance 3 5 surface be removed, even to the depth of only with my invention.

a few thousandths of an inch, the conductivity Fig. 2 represents in detail the resistance de- 8 5 of the body as a whole is largely reduced or, vice shown in Fig. 1. This device will be which is the same thing, the resistance inseen to consist of a pencil 1, having an outer creased. Theimportantfact, however, is that coating 2 and an interior portion shown in 4 whenalargenumber of theseresistance-bodies section at 3. The pencil is constructed by which differ largely in resistance among themmolding the same from a plastic mixture of 0 selves are treated in the manner described the clay or other earthy non-conducting or at resistances of the bodies become almost unileast poorly-conducting material with a minor form. I have discovered that the same result proportion of some conducting material, such 45 may be secured in a variety of wayssuch, as graphite, powdered carbon, carborundum,

for example, as by removing the exterior suror the like. Of the conducting substances face of the resistance devices by abrasion or mentioned I much prefer to use carborunby the application of heat. By the latter dum, since it more easily produces homogemethod, which I consider preferable, the reneous resistance material, due to the fact that a larger proportion of the same may be used than of graphite and also due to the fact that it may be obtained in an impalpable powder, while graphite is always more or less flaky.

After the rods or other resistance devices have been formed from the resistance material while in the plastic condition they are dried and then heated or burned, as above described, in an electric resistance mufl'le or other furnace until the conducting substance is burned away from the surface, leaving .an outer coating of more or less vitreous nonconducting substance. If desired, the rods may be baked preliminary to the burning off of the outer surfaceof conducting substance.

To make electrical connection with the conducting material of thepencil:whenthusxtreated byheat, various means may be employed. Thus the non-conducting surface may be removed and contact made with the exposedconducting portion. This is shown clearly in Fig. 2, in which the left-hand end 4 of the rod is cut away sufficiently to expose a cylindrical surface of conducting interior. If desired, the extreme end of the rod might be cut, or broken off and contact then made withthe exposed circular section of conducting material. In any case the contact I find may be much improved by applying ametal coating to thecontact-surface. I do this by;rubbing the surface with a soft metahsuch as lead, which by abrasive action of the surfaceisdeposited in the pores and forms a smooth adherent good-conducting coating. The surface, if cylindrical," may be revolved against the soft metal in a lathe orotherwise. A surface thus treated isintended toberepresentedat 4.

It has been found in practice thatinlightning-arresters making-use of theordinaryiresistance-rods theresistance of the rodsrafter a discharge has passed may besomuchhigher as to make the device useless so :far asany further protection is concerned. This may be due tothe actionof heat generatediin the rods in driving away moisture which may be present in the rods, or the heat may besufficientlylintense to, cause more or lessoxidation and wasting away of the carbon or other conducting material present in relatively high percentage in the outer skin of the rods. Rods made in accordance with my invention are not subject to. this disadvantage. Being provided with awveatherproof coating, they are not affected bymoisture, and havingzno.

outerskin of relativelyihigh conductivity they are not subject to permanent alteration of conductivity by heat.

What I claim as new, and desire to secure by Letters Patent of the United States, is-

'1. The method of producingartificial resistances which .COIlSlStS 1n comblning aconducting substance such as carborundum with a binding-materialsuchasclay,-=then baking the resistance device and subsequently burning away the outer surface of conducting materia 2. The method of equalizing the specific resistances of a plurality ofresistance devices formed of a mixturelofa conducting and a non-conducting material which consists in removing the surface coating of conducting ma- :terial.

3. The method of producing artificial resistances which consists in combining a conducting substance with a non-conducting binding -material,%forming the resultant mass while in rial .in the outer surface ofzthe-deviceszthus' molded.

'6. Themethodof producing an artificial high-.resistancebody,which con'sistslin combininga conducting substance witha relatively non-conducting'bindingmaterial, moldingthe material while plastic, baking, and mechani'callyafilling'the pores ofza selected portion of the surface. of the-body with some. soft metal.

.7. The :method'of applying ,a conducting coating toza porous resistance-body, which consistsinfillingthe pores of a selectedportion of thesurface of the body withmetal-by abrasive action between'the body and abody of themetal selected.

8. The method of applying a good electrically-conductingcontact-surface to-a body of porous or earthy material, which-consists in producing an abrasive actionbetween the body and a mass or body'of metal thereby causing adepositoflmetal Einthe pores of that portion of thesunface of saidbody ofporous or. earthyimaterial submitted to suchrabrasive action.

In witness-whereofiihave hereunto set :my hand this 15th :d ay. of November, 1901.

WILLIS R. WHITNEY.

Witnesses:

BENJAMIN HULL, HELEN ORFORD. 

